For example: I had a patron call my little small-town library looking for maps of the tunnels that supposedly connect my little town in Georgia with a much larger town in Ohio, with a stop at Crazy Phone Lady's childhood home in Pennsylvania. This connection was obvious to her because the towns have the same name, and her childhood home was on a street that was Trans[town name] Road. She was convinced that the term Underground Railroad was a literal railroad that was underground running through these tunnels that supposedly are under the entire US. She also claimed that her uncle who lived in a shack behind her childhood home was actually Nikola Tesla, despite the fact that Tesla had been dead for a decade or more before she was born.
Along the way, she rambled on about how the Philadelphia Experiment movie was a way to discredit the truth that the USS Eldritch really did disappear, travel through dimensions, and then reappeared, Edison was a thief (true enough) and on and on and on... I finally had to lie that there was a patron at my desk needing help to get her to shut up long enough to disconnect.
How do you deal with someone like that, who is way the hell out of her mind and rambling on and on? What do you do when the crazy patron in question shows up physically in the library instead of calling, and thereby being easy to either gently disengage by claiming another patron or just hanging up? I'm not worried about CPL showing up, she was calling from across the country, but I'm curious if any of you have some suggestions for when the crazy walks into the library.